Composite materials are those materials that associate at least two materials of specific mechanical characteristics, which results in a third material with the desired mechanical properties. Normally, composite materials result from the association of a polymer with a strengthening material, generally a fiber, whether synthetic, of mineral or vegetal origin. The state of the art reveals a plurality of composite materials built by different polymer classes associated with different types of fibers, such as glass fiber, rock fibers, mineral wools, natural fibers etc.
Particularly, the state of the art reveals composite materials made of polymer of the polyolefin class, such as the polypropylene or the polyethylene terephthalate, associated with natural fibers, such as sisal fiber, cocoa fiber etc.
Currently, the process for the preparation of composite materials through the association of a polymer and a natural fiber is carried out by molding, which considerably limits the form of the composite material and, consequently, its commercial application. As it is clear for those skilled in the art, the molding process allows the manufacturing of objects with limited structure and form, thus reducing the applications of the composite material.
Until today, an injection molding process has not been effectively carried out for composite materials made of polymers and natural fibers. This limitation to the molding process is associated to several difficulties of the injection process. Firstly, due to the hygroscopic and hydrophilic nature of the natural fibers, there is a tendency of humidity absorption, which generates the formation of gas during the injection process. This is because, due to the injection process, volatile gases are formed that are locked in the interior of the injection unit (gorge and screw), when the dosage step takes place (speed of the screw×contra-pressure), and inside the cavity of the mold during the injection molding cycle. Consequently, a product is formed with porosity and microstructure similar to an expanded structure. Moreover, the distribution of porosity is influenced by the processing conditions during injection (such as pressure, temperature, and time), and consequently compromises the mechanical properties of the material.
Therefore, it is an object of the present invention a process for the preparation of a composite material that overcomes the deficiencies of the processes found in the state of the art.
More particularly, it is an object of the present invention to present an adequate material to be molded in an injection process resulting in a composite.
Another object of the present invention is a process for the preparation of a composite material that is comprised of a thermoplastic polymer, particularly a polyolefin, associated to natural fibers.
Another object of the present invention is an injection process for a composite material comprising a thermoplastic polymer, particularly a polyolefin, associated to natural fibers.
Another object of the present invention is the composite material prepared by the injection process in accordance with the present invention that is particularly adequate for the manufacture of automotive spare parts.